I've been developing a simple physics engine as a side project for a while, but I've been stuck on an issue when incorporating large amounts of bodies. When I start using around 50+ rigid bodies in my scene, some bodies seem to gain velocity from nowhere, and get shot off to the side, and eventually all of the bodies disappear.

For collision, I'm using a simple AABB:

struct AABB
{
Math::Vector2 center;
Math::Vector2 hSize;

AABB() = default;
AABB(const Math::Vector2& _center,
const Math::Vector2& _hSize)
:
center{_center},
hSize{_hSize}
{}
};

My broadphase is a quadtree, and I'm using impulses for collision resolution:

Math::Vector2 relativeVelocity {
contact->bodies[1]->linearVelocity - contact->bodies[0]->linearVelocity
};

float normalVelocity { relativeVelocity * contact->normal };
if (normalVelocity <= 0) return;

float e { std::min(contact->bodies[0]->restitution, contact->bodies[1]->restitution) };
float totalInvMass { contact->bodies[0]->invMass + contact->bodies[1]->invMass };

float j { -(1.0f + e) * normalVelocity / totalInvMass };

Math::Vector2 impulse { contact->normal * j };
contact->bodies[0]->linearVelocity -= impulse * contact->bodies[0]->invMass;
contact->bodies[1]->linearVelocity += impulse * contact->bodies[1]->invMass;

And a position solver:

constexpr float slop { 0.01f };
constexpr float percent { 0.8f };

Math::Vector2 correction {
contact->normal * percent * std::max(contact->intersection - slop, 0.0f) /
(contact->bodies[0]->invMass + contact->bodies[1]->invMass)
};

contact->bodies[0]->position -= correction * contact->bodies[0]->invMass;
contact->bodies[1]->position += correction * contact->bodies[1]->invMass;

My physics engine step is applying gravity to bodies that are affected, integrate the bodies, collision/detection+resolution, then clear forces.

Is there any reason I would be having an issue?

Where did you get your physics relations from ?

@Gotanod I'm currently just using the time between frames, I don't have a fixed step atm. I've tried reducing gravity before too